Python OpenCV using Notes (ii) (Simple geometric image drawing)

Simple geometric images generally include points, lines, matrices, circles, ellipses, polygons, and so on. First of all, recognize OpenCV's definition of pixel points. One pixel of the image has 1 or 3 values, a grayscale value for the grayscale image, and a pixel value of 3 values for the color image, showing a different color.
Then there is a point to make a variety of polygons.

(i) Draw a line first

Function: Cv2.line (img,point pt1,point pt2,color,thickness=1,line_type=8 shift=0)
The representative with a value has a default value, which does not have to be given. You can see that this function mainly accepts the coordinates of the parameter two points, the color of the line (color image is a 1*3 array) as follows:

import cv2importas npfromimportas pltimg = np.zeros((512,512),np.uint8)#生成一个空灰度图像cv2.line(img,(0,0),(511,511),255,5)plt.imshow(img,‘gray‘)

import cv2importas npfromimportas pltimg = np.zeros((512,512,3),np.uint8)#生成一个空彩色图像cv2.line(img,(0,0),(511,511),(155,155,155),5)plt.imshow(img,‘brg‘)

(ii) Draw a rectangle

Functions: Cv2.rectangle (IMG, (380,0), (511,111), (255,0,0), 3), need to determine the two points of the rectangle (upper left and bottom right), color, the type of line (not set to default).
For example:

import cv2importas npfromimportas pltimg = np.zeros((512,512,3),np.uint8)#生成一个空彩色图像cv2.rectangle(img,(20,20),(411,411),(55,255,155),5)plt.imshow(img,‘brg‘)

(iii) Draw round

It is also simple to draw a circle, just to determine the center and radius, the function:
Cv2.circle (IMG, (380,0), 63, (255,0,0), 3), such as:

import cv2importas npfromimportas pltimg = np.zeros((512,512,3),np.uint8)#生成一个空彩色图像cv2.circle(img,(200,200),50,(55,255,155),1)#修改最后一个参数plt.imshow(img,‘brg‘)

import cv2importas npfromimportas pltimg = np.zeros((512,512,3),np.uint8)#生成一个空彩色图像cv2.circle(img,(200,200),50,(55,255,155),8)#修改最后一个参数plt.imshow(img,‘brg‘)

(d) Draw an ellipse

The

Ellipse is more complex, involving the long axis short axis, ellipse center, rotation angle, and so on, see the OpenCV Reference manual:

Image as follows:

An example is as follows:

import  cv2import  numpy as  npfrom  Matplotlib import  pyplot as  pltimg = Np.zeros (( Span class= "Hljs-number" >512 , 512 , 3 ), np.uint8)  #生成一个空彩色图像  cv2.ellipse (img, 256 , Span class= "Hljs-number" >256 ), (150 , 100  ), 0 , 0 , 180 , Span class= "Hljs-number" >250 ,-1 )  #注意最后一个参数-1, Indicates that the image is populated, is not populated by default, and if omitted, only the ellipse outlines the  plt.imshow (img,)  

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Python OpenCV using Notes (ii) (Simple geometric image drawing)